The performance of an internal combustion engine, such as, for example, a diesel, gasoline, or natural gas engine may be impacted by the conditions under which the engine is operated. For example, the performance of an internal combustion engine may change as the altitude at which the engine is operated increases. In particular, the operation of the engine at higher altitudes may cause a decrease in fuel efficiency and/or an increase in the generation of undesirable emissions.
The impact of altitude on engine performance results from the decrease in air density and air pressure at higher altitudes. The decrease in air density and air pressure at higher altitudes causes a reduction in the air-fuel ratio provided to the engine, a reduction in the efficiency of an associated turbocharger system, and a reduction in the combustion efficiency within the engine. The reduction in each of these parameters may result in a decreased fuel efficiency and/or increased emission generation.
Generally, an internal combustion engine operates on a selected air-to-fuel ratio regardless of the altitude at which the engine is operating. The operating air-to-fuel ratio is selected to meet certain fueling and power requirements and may depend upon the current engine speed and load. The selected air-to-fuel ratio may be achieved by actuating the engine valve for a certain period of time and by injecting a certain amount of fuel into a cylinder. However, when the engine is operating at a high altitude where the air density and pressure is reduced, less air will pass by the engine valves during a given time period. Accordingly, the air-to-fuel ratio supplied to the engine will decrease as the altitude of operation increases.
The air-to-fuel ratio is a critical component of an internal combustion engine, such as, for example, a diesel engine. A reduction in the air-to-fuel ratio typically translates to a reduction in the efficiency of combustion. Usually, the reduced air-to-fuel ratio reduces the rate of combustion and also reduces the amount of the combustion energy that may be translated to mechanical work. When less combustion energy is translated to work, the fuel efficiency of the engine decreases and the temperature of the exhaust gas increases.
A turbocharger system may be added to the internal combustion engine to improve the performance of the engine. The turbocharger system recovers energy from the exhaust stream and uses the recovered energy to increase the pressure of the air in the intake stream. The increased intake air pressure may result in more air being pushed into the combustion chamber and thereby increase the air-to-fuel ratio.
However, under standard operating conditions, a typical turbocharger system is approximately 60-65% effective, which means that only 60-65% of the recovered energy is applied to the intake air flow. The lower density of the air at high altitudes further reduces the efficiency of the turbocharger. Thus, not all of the increased exhaust gas energy is translated to increased intake manifold pressure. Accordingly, the turbocharger will not compensate for all losses associated with operating at higher altitudes.
The system and method of the present invention solves one or more of the problems set forth above.